The present invention relates to pulp dewatering presses, and particularly relates to presses comprising two press rolls for pulp dewatering.
Pulp dewatering presses are used to increase the dry solids content of pulp suspensions from some lower percent to 40-50 percent. A press comprises two press rolls located in a trough to which a suspension of pulp is supplied. The press rolls are provided with perforated shell surfaces through which dewatering takes place. On a perforated shell surface, a pulp layer is formed which, by rotation of the rolls, is passed into the nip between the rolls. The extent of dewatering and resulting solids concentration of the pulp can be determined by controlling the speed of the rolls, the pressure difference over the pulp web on the perforated surface, and the distance between the rolls, which is defined as the nip.
The shell surfaces of the press rolls usually are manufactured of perforated sheet metal to resist the high pressures arising in the nip. The maximum pressure in the nip occurs in a linear direction where the nip is narrowest. Too high a linear pressure, however, can damage the fibers in the pulp, and this high pressure places higher stress on the equipment.
To prevent damage to both pulp fibers and the dewatering equipment, it is desirable in the dewatering of many pulp suspensions to distribute the maximum pressing force over a greater surface area. This is accomplished through the use of press rolls with surface elasticity. In the past, equipment manufacturers have attempted to obtain surface elasticity simply by providing conventional press rolls with an elastic shell surface. However, because of the pressure involved, these elastic shell surfaces were subject to wear and deformation at a greater rate than conventional press roll surfaces.
A pulp dewatering press is desired wherein one or both press rolls have a resilient surface yet resist wear and deformation in a manner comparable to the surfaces of conventional nonresilient press rolls used in such presses.